A:
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and capable culprits. Yet, others think staff members play some, albeit small, role. You
can torture us with your plant questions, but we will never reveal the Green
Guru's secret identity.

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Sunday - September 13, 2009

QUESTION:

Bought and had nursery install a 4" diameter, 16' tall chestnut oak. Watered it as instructed-every 2nd or third day-hose stream size of my pinky for 45-60 minutes. It was planted in July. Just last week the leaves turned yellow and then brown, some have fallen off. The location has very little topsoil and is limestone underneath, it is mulched. Do you think it is transplant shock? Is it already a goner? Will it survive a WI winter? The older/larger English oak planted at the same time, same conditions is doing very well--new growth continues to appear. Thanks!

ANSWER:

The first thing we do when we receive a question about specific plants is to research their nativity, so we can get accurate information. The Lady Bird Johnson Wildflower Center is dedicated to the use, care and propagation of plants native not only to North America but to the area in which they are being grown. We learned that Quercus prinus (chestnut oak) is not native to Wisconsin, but mostly to areas south and east of there. Quercus robur, English oak or white oak, on the other hand, is not even native to North America, but to temperate areas of Asia and Europe, so we will have no information on it in our Native Plant Database.

Since it is the Chestnut Oak about which you are concerned, let us refer you to this USDA Forest Service website on Quercus prinus. You should read all of it, but some points we were interested in is that it is naturally found in poor, dry, sandy or rocky landscapes, but is not suited to clay or poorly drained soil. Another consideration is that it is hardy from USDA Hardiness Zones 5 to 9a. The best we can tell is that Waukesha County is in Zones 4b to 5a (average annual minimum temperatures -10 to -20 deg), so it could be marginal there, but since you have not yet experienced cold weather, we can't blame the leaf drop on that. Cold hardiness is variable and even mature trees are sometimes killed by a hard winter freeze. We received this question from you on September 9, and have to assume that even though in Texas we were still having 100+ degree temperatures and are in extreme drought, it must be beginning to be Fall in Wisconsin. So the yellowing and browning of the leaves could be quite natural. We're not sure we would have tried to transplant a tree that large, especially in mid-Summer, even in Wisconsin, but that is hardly something you can undo. We wouldn't write it off as a goner, nor trim off upper growth as we sometimes recommend for transplant shock. Right now, it needs all the leaves it has to continue to manufacture food to be stored up in the roots for the winter. Will it survive a Wisconsin Winter? That depends on so many variables, like the condition of the roots when the tree was planted and whether or not there are severe freezes, that we really couldn't guess.

Hopefully, the tree will pull through. We would just recommend that the next time you have a tree planted you select one native to your area and therefore well-adapted to your climate, soils and temperatures. We would recommend not trying to plant quite such a large tree, and always checking to make sure it is not rootbound in its pot. Any plant that has been in a sheltered greenhouse or plant lot location for some time is going to have shock when it gets out into the real world and real dirt. Always insist in a recently-dug tree and on removing the pot so you can check that it does not have roots wrapped round and round in the shape of the pot. Beyond that, check the drainage in your soil. As mentioned above, this tree does not tolerate clay soils or poor drainage very well. If, when you are doing your watering, the water stands on the soil a while, you probably have either clay soil or poorly draining soil or both. Drowning the roots can be a death blow to a tree already struggling.

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